In a cellular deployment, scrambling sequences are controlled by the eNodeB such that both the User Equipment, UE, and the eNodeB always know what scrambling sequence is applied by each LIE and for each channel and resource. However, for device-to-device, D2D, communication, a central node performing scheduling and controlling all UEs in proximity is lacking, e.g., for Out of network Coverage, OoC. Furthermore, UEs in proximity might be controlled by different eNodeBs or control nodes. Because of the above, UEs may be unaware of the scrambling sequences used by neighbor UEs when transmitting their channels/signals.
In 3GPP LTE, the device only needs to de-scramble sequences form the serving cell. D2D broadcast communication introduce some new aspects of the lower layer scrambling, mainly how to handle—from a device complexity point of view—the case of a device OoC and capable to receive D2D broadcast communication, or a D2D discovery signal. A device OoC may not have information of scrambling sequences used for the D2D broadcast communication and in order to reduce such device scrambling search space an efficient scrambling procedure is needed. Furthermore in D2D communication a device should also be able to receive broadcast communication from other devices in another cell than the receiving device. This put also requirements on the device to be able to descramble sequences for many different cells, and an exhaustive search over all potential scrambling sequences is very complex.
Therefore there is a need for methods and apparatus for efficient scrambling identification while still fulfilling the requirements of randomized sequences and identification of sequences destined for a particular device.